The present invention relates to the field of firearms and, more specifically, to the field of firearm cartridges.
A cartridge provides ammunition for a firearm. It normally includes a casing, a projectile associated with the casing, an ignitable propellant that when ignited propels the projectile away from the casing through the barrel of the firearm, and a primer that ignites the propellant. The ignitable propellant ordinarily ignites upon the application of heat as with, for example, ordinary gunpowder (i.e., potassium nitrate, wood charcoal, and sulfur in the approximate proportions of 6:1:1 by mass). The propellant responds to heat by suddenly forming hot expanding gases that causes a contained explosion that propels the projectile from the firearm. The primer normally is a percussion impact or pressure sensitive compound that ignites in response to shock or pressure. In firing, a striker or firing pin usually a small rod or hammer causes a shock and/or pressure that ignites the primer. When ignited, the primer expels hot particles or gas. The heat generated by ignition of the primer in turn ignites the propellant causing the sudden formation of hot expanding gases result in the contained explosion that propels the projectile from the firearm.
The cartridge combines into a single self-contained system each of the elements that must be included either as part of the ammunition or the firearm itself for successful firing. By contrast, each of these elements had to be separately loaded in flint-lock and percussion cap firearms which were the only available firearms up through the middle of the nineteenth century. By incorporating each of these items in a stand-alone, easily loaded module, the cartridge has made the firearm more potent and more practical. The cartridge has been perhaps the most important factor contributing to the advances in small arms technology that began in the latter half of the nineteenth century.
Notwithstanding its significant advantages, problems with the conventional firearm cartridge remain. Foremost among these is the risk that the ignitable substance forming the primer will fail. For example, a defect in the manufacture of the substance might render it inoperable before it is positioned within the cartridge casing. Even if the primer substance is free of defect and operable when first put into the cartridge, there remains the risk that it might later be rendered inoperable. For example, moisture could enter the portion of the cartridge where the primer is placed. The possibility that this might occur is higher the more harsh the conditions under which the firearm and cartridge are used such as in a wet or swampy area. Because the primer is most efficiently placed near the proximal end surface of the cartridge casing, there is a greater possibility the primer will be damaged than will the propellant, which is ordinarily ensconced in a medial portion of the casing between the projectile and the proximal end of the casing.
Because, again, the primer is positioned most efficiently near the proximal end surface of the cartridge there also is the risk that rather than moisture seeping in, the primer substance could seep out due to a small hole or other defect in the casing. Whatever, the cause, the fact remains that if the primer substance is or becomes inoperable, the cartridge will misfire or far more likely not fire at all. The later is commonly referred to as cold shot. Specifically, if the primer substance, for whatever reason, is inoperable, the primer will not ignite and, hence, neither will the propellant, thus leading to a failure of the firearm to fire.
There have been efforts to address some of the firing problems inherent in conventional firearm cartridges. For example, U.S. Pat. No. 5,148,749 to Maes et al., titled Priming Chamber For A Firearm Cartridge. Maes et al., attempts to improve the conveyance of heat from a primer chamber to a main charge (i.e., powder) in the cartridge by positioning an anvil and flash holes in the primer chamber. Maes et al., however, fails to address the problems associated with misfire as described above. U.S. Pat. No. 4,378,739 to Klein et al., titled Primer Firing Means, does attempt to enhance firing reliability, but requires the replacement of a firing pin mechanism with use of a shockwave, high-pressure gas that is propelled by a detonating chord. Thus, the Klein et al. device is unworkable in the context of a standard firearm which fires a cartridge having a casing and a projectile positioned at least partially therein and which requires detonation using a firing pin.
In an unrelated context, U.S. Pat. No. 1,491,000 to Brandt et al., titled Torpedo, suggests an improvement to the fuse used to launch a torpedo. Brandt et al. attempts to reduce the possibility of cold shot by using two primer caps. Upon detonation, each primer cap releases heat or pressure which is then conveyed along angled passageways to a central tube and onward to the end of the tube where there is positioned an ignitable substance adapted to blow out an end cap and ignite a slow burning fuse. The primer caps are ignited when struck by a multi-pronged striker that, until firing, remains spaced apart from the primer caps. The features of Brandt et al., like those of Klein et al., however, are ill-suited for adaption to a firearm. The features which may work well for a torpedo pose distinct disadvantages for the cartridge of a firearm. Among these are the specific primer cap detonator that must be used. The multi-pronged structure is more complicated and costly to manufacture, while the need to space it apart from the caps to be detonated slows down firing time. The problem of slowed firing time, moreover, is exacerbated by the fact that the device also relies on a slow burning fuse for firing.
Moreover, Brand et al. presents other features that themselves can increase the risk of cold shot. Specifically, the indirect conveyance of heat from the primer caps via angled passages that must merge into a single long tube not only further reduces firing time, but also presents the risk that particles may lodge at one of the bends of the angled passages. If the lodged particles clog the single tube, there is no alternative means of conveying the heat needed for firing. If this occurs, the result is a cold shot.
In light of these limitations on other devices, there remains a significant need for a cartridge usable with a standard firearm that provides reduced delay in detonation and enhanced reliability in firing.
With the foregoing in mind, the present invention advantageously provides a multi-ignition cartridge that has substantially reduced chances for misfire and cold shot. The multi-ignition cartridge, moreover, further provides for rapid firing by ensuring that the time lapse between impact of the firearm""s firing pin of the firearm""s on the multi-ignition cartridge and the firing of a projectile from the cartridge is kept to a minimum. Moreover, the multi-ignition cartridge achieves these distinct advantages while nonetheless being relatively easy and cost efficient to manufacture.
According to the present invention, the multi-ignition cartridge includes a cartridge casing and at least one projectile adapted to be positioned at least partially within the casing. The cartridge casing further includes at least two separate chambers formed in the casing. Each chamber, moreover, is in fluid communication with a separate interior cavity formed in the cartridge and in which the at least one projectile can be at least partially contained. The outer surfaces of each chamber form portions of the surface of the cartridge casing. A strike plate is positioned to contact each surface portion corresponding to each chamber. Preferably, the strike plate abuttingly contacts each surface portion.
Each separate chamber contains an ignitable substance. When the strike plate is struck by the firearm""s firing pin, the strike plate rapidly compresses the outer surface portions that correspond to each chamber. The rapid compression increases the pressure in each chamber thereby igniting the ignitable substance in at least one of the chambers. Ignition creates a rapid expansion of hot gases. Because each chamber is in fluid communication with the interior cavity, the heat is conveyed to the interior cavity. The heat is sufficient to ignite a main charge positioned in the interior cavity. When the main charge ignites, it, too, causes a rapid expansion of hot cases leading to an explosion that propels the projectile away from the casing and through the barrel of the firearm.
Because the multi-ignition cartridge contains a plurality of chambers having an ignitable substance, it is only necessary that the substance in one of the chambers ignite in order to fire the cartridge. Because the strike plate is positioned to impact and compress each chamber when the strike plate is struck once in one location by a firing pin, each chamber""s pressure is increased, and it is only necessary that the substance in any one of the chambers ignite to set off the reaction that propels the projectile. Accordingly, the risk of misfire or cold shot is substantially reduced. Indeed, the probability of misfire and cold shot can be reduced in proportion to the number of additional chambers added to the cartridge according to the present invention.
A further advantage of the multi-ignition cartridge lies in the fact that the single strike plate can be positioned to abuttingly contact the corresponding surfaces of each chamber. Because there is no gap between the strike plate and surface portions of the casing corresponding to each chamber, firing is more rapid. Specifically, the impact of the firing pin on the strike plate immediately compresses each chamber and increases the pressure in each thereby igniting the ignitable substance therein. Thus, the multi-ignition cartridge not only reduces the chances for misfire and cold shot, it also ensures that the rapidity with which the cartridge fires is not reduced in order to be made more reliable.
Moreover, firing by impacting the strike plate is achieved even though the strike plate need only contact portions of each outer surface of the chambers containing the primer. Specifically, the surface portions can be arrayed on each side of a point substantially centered on the proximal end of the casing, preferably at equal distances from the center point. The strike plate preferably, then, preferably is formed to have a rectangular body that contacts only a part of each surface portion. More preferably, the surface portions lie in a single plane against which the strike plate is positioned as described above. This not only provides the advantages related to rapid firing as already described, but also makes the multi-ignition cartridge easier and more efficient to manufacturer, especially in terms of materials costs.
The rapidity with which firing is achieved is further enhanced through the means by which heat is conveyed from each chamber to the interior cavity. Specifically, the heat is preferably conveyed via direct, substantially linear passages positioned between the interior cavity and each corresponding chamber. Because heat flow is direct rather than indirect as in other devices, the time lapse between ignition of the ignitable substance in at least one chamber and the ignition of the main charge in the interior cavity is accordingly kept to a minimum.
The present invention further provides a method of propelling a projectile from a cartridge casing that is both rapid and more reliable. Specifically, firing is done by simultaneously increasing the pressure within a plurality of separate chambers formed in the casing and igniting a preselected ignitable substance positioned within at least one of the chambers. Upon ignition, the heat generated is conveyed to a bore formed in the casing to thereby ignite a combustible material positioned in the bore, the resulting contained explosion thereby propelling a projectile positioned at least partially within the bore away from the casing and through the barrel of the firearm. Accordingly, firing time is rapid in that heat is conveyed directly, while firing is more reliable in that the ignitable substance in only one of the separate chambers need ignite in order to propel the projectile from the cartridge casing.
A related method for enhancing firing and reducing the chances of misfire and cold shot in a firearm includes striking a strike plate of a cartridge, in which the strike plate has a substantially flat inner surface such that, the substantially flat surface of the plate then simultaneously strikes outer surface portions of at least two chambers in each of which is positioned an ignitable substance. The ignitable substance in at least one chamber is thereby ignited resulting in the generation of heat in the at least one chamber. Further, heat generated by the ignition of the ignitable substance is conveyed directly to a substantially hollow bore containing another ignitable substance and a projectile. When the second ignitable substance ignites, the ensuing explosion propels the projectile away from the cartridge and through the barrel of the firearm. Thus, the method aspects of the present invention, like those of the apparatus already described, reduce delay in detonation and enhance reliability in firing the cartridge in any type of firearm.